1. Field of the Invention
The present invention relates to a device for varying a stroke.
2. Description of the Related Art
In a known device for varying a stroke, the device comprises two interconnected cylinders. One of the cylinders has a diameter larger than the diameter of the other cylinder, and two pistons each having a diameter matching the different diameters of the two cylinders are inserted in the respective cylinders. The cylinder chamber formed between the pistons in the cylinders having different diameters is then filled with oil (Japanese Unexamined Patent Publication No. 48-4823). In this device, the piston having a larger diameter than the other piston is actuated by an actuator and, at this time, the smaller diameter piston is moved by a stroke greater than that of the larger diameter piston.
However, in this device, since the oil in the cylinder chamber is forced out of the cylinder chamber via the clearance between the larger diameter piston and the larger diameter cylinder or via the clearance between the smaller diameter piston and the smaller diameter cylinder, a problem arises in that an oil supply device must be provided to feed replacement oil into the cylinder chamber. In addition, another problem arises in that measures must be taken to prevent the formation of air bubbles in the oil in the cylinder chamber.